Ischemia is the lack of oxygen supply to cells. In animals, including humans, the underlying cause of ischemia is typically a cardiovascular disease, where blood vessels may be affected by atherosclerosis. Cardiac ischemia is caused by restriction of blood flow in the coronary arteries, e.g. due to atherosclerosis. This reduced blood flow and the resulting lack of oxygen to the myocytes in the heart may lead to several effects, including contractile dysfunction and hibernating cells. These various effects may in turn decrease the hemodynamic performance of the heart, which ultimately can result in worsening heart failure and further decrease in pumping capacity.
Ischemic heart disease (IHD) is very common. IHD may be symptomatic, such as in angina pectoris, causing the patient to experience severe discomfort and pain. However, a majority of ischemic periods are silent and therefore hard to detect and classify. Most ischemic episodes, regardless of being symptomatic or silent, are reversible but still influence the risk of arrhythmias, the functional state and long-term remodeling of the heart.
A common technique in the art to detect cardiac ischemia is to measure oxygen saturation (SO2) in coronary sinus blood, such as disclosed in U.S. Pat. Nos. 5,156,148; 5,199,428; US 2005/0154370; US 2008/0177194 and EP 1 386 637. These prior art documents generally state that cardiac ischemia is detected as a decrease in SO2 in the coronary sinus blood.
Prior art techniques that perform ischemia detection based solely on a reduction in SO2 in coronary sinus blood run a risk of classifying non-ischemic events as cardiac ischemia. Hence, there is a need for a more accurate cardiac ischemia detection.